A nice homage to old school dungeon crawlers.
Exploration: Very good. Uncovering secret locations and solving puzzles had me interested to see what was next.
Puzzles: This is where the game excelled. Started off very simply, but there were some quite challenging. There were some that required moderately quick reflexes or good timing, along with puzzles that challenged your brain. I admit to getting help about 4 times throughout the game, but after getting the answer felt I should have figured it out on my own.
Combat: While challenging, combat was mostly a test of your strafing and movement skills instead of requiring much in the way of strategy. By far the low point of the game for me. It wasn't that combat was horrible, it just didn't really add much in the the way of fun.
My full review can be found at: http://www.oneguytoomanygames.com/2012/04/legend-of-grimrock-review.html